It is well known in different fields to provide the output stages in electrical circuits with short circuit and overload protection of different kinds. With respect to output stages including two series connected transistors with the output between the transistors, it is known to have short circuit or overload protection for one or both transistors controlled by the potential on the output between them. It is also pertinent to the prior art to limit the current through the transistor in the output stage in connection with short circuiting or overloading by activating the input signal in a final stage in a current-decreasing direction with the aid of transistors and feedback. It is also known, per se, to have series connected transistors in short circuit or overload protectors, the conductive capacity of the transistors being directly or indirectly controlled by input signals to, or output signals from a circuit which is to be protected.
Short circuit and/or overload protection for series connected transistors in different fields which may be of interest in connection with the present invention will be apparent from e.g. the following publications: U.S. Pat. No. 3,447,035, U.S. Pat. No. 3,648,071, U.S. Pat. No. 3,749,936, U.S. Pat. No. 3,786,364, DE No. 2947062, DE No. 3103852, EP No. 0083504 and EP No. 0091203.